Brazil's government has been aggressively promoting its ethanol industry, seeking to capitalize on high fuel costs by selling the fuel derived from various crops like corn and sugar. In the drive to triple the volume of ethanol exports, Brazil has signed multiple international energy agreements, most notably with the US, its biggest customer. President Luiz Inacio Lula da Silva's effort to expand ethanol production has faced criticism externally from Latin American leaders like Venezuela's President Hugo Chavez and Cuba's President Fidel Castro and internally from poor people's movements and environmentalists. Among these criticisms are assertions that using food crops for fuel could lead to a food-price crisis for millions of poor people and that monoculture could exacerbate Brazil's already-chronic economic inequality and environmental problems.